Graft copolymers

ABSTRACT

A process for the production of a graft copolymer comprises reacting an irradiated polymer in a reaction mixture comprising a first phase and a second phase. The first phase comprises a source of at least one non-water soluble monomer and the second phase comprises water and optionally, a water miscible organic solvent. The first and second phases are substantially immiscible and non-emusifiel. A high degree on monomer conversion is achieved.

This application is the U.S. National Phase application of InternationalApplication No. PCT/GB01/04637.

This invention relates to an improved process for the preparation ofgraft copolymers using radiation induced grafting and to graftcopolymers made by such a process. The invention also relates to thegraft copolymers so produced as supports for catalytically activespecies.

The technology of modifying the properties of polymer materials hasinterested chemists since the beginning of the nineteenth century. Earlydevelopments included the modification of rubber by isomerisation withacid and by vulcanisation with sulphur. These developments inspiredchemists to more systematic work in applying organic chemistry pathwaysto modify the surface or bulk properties of polymers. To date a largenumber of synthetic polymers have been prepared and a number ofdifferent techniques have been developed to change or improve theproperties of polymers. The chemical modification of polymers has-becomea wide domain of polymer science and techniques such as coronadischarge, plasma and grafting are frequently employed for modification.

Generally, any reaction of classical organic chemistry can be applied tomodify or functionalise a polymer and reactions can be carried out insolution, in the melt or in the solid state. Cis-trans isomerisations ofpolydienes, cyclisation of polyacrylonitrile, addition of maleicanhydride onto double bonds, and hydrolysis of polyvinyl acetate topolyvinyl alcohol are examples of reactions that can be carried out insolution.

During the last twenty years, the modification of polymers usingradiation has become very important in polymer science and technology.The breakthrough in the industrial use of radiation took place in the1950's with the discovery of the crosslinking of polyethylene using highenergy radiation. Today the changes induced by radiation on theproperties of the most common polymers are well studied and documented.Applications such as radiation stabilisation and radiation inducedpolymerisation, crosslinking and grafting have gained central industrialimportance.

Irradiation leads to the formation of reactive species in the polymersbeing irradiated. This can initiate chemical reactions. The process ofgrafting, whereby side chains are attached to a host polymer, can beinitiated by irradiation. The grafted polymer has distinctivelydifferent properties than those of the original polymer. If the sidechains comprise dissimilar monomer units to the host polymer, then thepolymer is a copolymer, whereas a homopolymer is formed when the monomerunits and the host polymer are similar. Among the different graftingtechniques (TV, plasma, chemical initiation) graft copolymerisationinduced by high energy radiation offers an attractive method ofpreparing new polymers for novel applications.

Most radiation grafting reactions utilise free radicals formed duringirradiation, and occur by a free radical mechanism. Ionic graftingprocesses using ionising radiation are possible but are restricted bythe need to use high vacuum and extremely dry experimental conditions.

Historically, radiation grafting has used low dose rate gamma rays from⁶⁰Co sources. During the past 10 years however, there has been muchinterest in using high energy electrons from accelerators with high doserates. High dose rates make radiation grafting processes commerciallymore attractive.

There are three common methods of radiation grafting: mutual,pre-irradiation and peroxide methods. In mutual (or direct) grafting,the polymer is irradiated in the presence of the monomer. This is asimple and effective method since the free radicals initiatepolymerisation immediately as they are generated. The disadvantage ofthis method is however, that simultaneous graft copolymerisation andhomopolymerisation occurs upon irradiation. This reduces the yield ofthe desired copolymer. There are limited possibilities to alter theratio of graft copolymerisation versus homopolymerisation for example,by the addition of compounds such as Mohr's salt or Fedl₃, or by thecareful choice of the polymer-monomer system.

In a pre-irradiation process, the polymer is irradiated in an inertatmosphere and is subsequently immersed in a monomer solution. Theprocess requires additional steps in comparison to direct grafting, buthas the advantage that only a small amount of homopolymer is formed,mainly by a chain transfer process. The grafting process is initiated bytrapped radicals that are formed during irradiation and is controlled bythe diffusion of the monomer into the polymer. It can be facilitated bythe use of solvents that are able to swell the graft copolymer formed.

The peroxide process follows much the same process mechanism aspre-irradiation grafting. The main difference is that the polymer isirradiated in the presence of oxygen, thus forming peroxides andhydroperoxides that are stable and can be stored in the polymer for along period of time. Grafting is activated by cleavage of the peroxidesor the hydroperoxides by heat, UV-light or catalysis in a monomersolution.

One of the main concerns using radiation grafting on a production scaleis achieving a high conversion of the monomers used for grafting. A highconversion is not only is economically desirable, but also decreases theamount of waste material to be disposed of, and minimises the need formonomer recycling. It is clearly desirable to develop radiation graftingprocesses with high monomer conversion.

WO 00/15679 describes a water based grafting process in which monomerunits are grafted onto a cross linked polymer from a reaction mixturewhich comprises an emulsion of the monomer in water. Emulsifiers such asalkyl sulphates and fatty acid esters are used in relatively highproportions of up to 15 wt % of the reaction mixture in order to improvewetting of the polymer and the stability of the emulsion.

U.S. Pat. No. 5,817,707 describes a process for making a graft copolymerof a porous propylene polymer and a vinyl monomer. The reaction mixtureincludes water and a surfactant. The function of the surfactant is toproduce an emulsion with water-immiscible monomers by forming stablemicelles, as well as improving the solubility of the monomer in theaqueous phase. The surfactants may be an anionic, cationic or non-ionic.

A novel grafting process with significantly increased monomer conversionhas been developed. The monomer solutions used in the pre-irradiationand peroxide grafting processes contain monomers immiscible in water.The process of the invention is effective during grafting of such waterimmiscible monomers. If water is added to these solutions, two separatephases are formed. When irradiated polymer fibres are added to themonomer solutions, the fibres are forced into the phase containing themonomers. This leads to a dramatic increase in monomer conversion.Thorough agitation of the solution is also beneficial to high monomerconversion

Accordingly, the invention provides a process comprising reacting anirradiated polymer in a reaction mixture comprising a first phase and asecond phase; wherein the first phase comprises a source of at least onenon-water soluble monomer; wherein the second phase comprises water; andwherein the first and second phases are substantially immiscible andnon-emulsified.

Preferably, the second phase further comprises a water miscible organicsolvent.

The invention further provides grafted copolymers made by such aprocess.

Suitable polymers include polyolefins and fluorinated polyolefins,particularly polyethylene, but other polymers may also be considered,and the invention applied advantageously to such polymers.

The polymer may be in any form, including especially beads and fibres,although there may be technical interest in other forms such as films.

The monomers in the reaction mixture may comprise any non-water solublemonomers however preferably, the monomers are selected from the group ofstyrene and derivatives, vinyl benzyl derivatives such as vinyl benzylchloride, styryl diphenyl phosphine, vinyl benzyl boronic acid, vinylbenzyl aldehyde and derivatives, α-methyl styrene, α-methyl styrenederivatives such as m-isopropyl-α,α-dimethyl benzyl isocyanate, vinylacetate, vinyl pyridine and vinyl sulphonic acid. If the reactionmixture comprises more than one type of monomer, the resulting polymerwill have varied monomer units.

Suitably, water comprises from 5 to 80% by weight of the reactionmixture, preferably between 20 and 50% by weight.

Suitably, the water miscible organic solvent comprises an alcohol oranother water miscible solvent and preferably, the water miscibleorganic solvent comprises ethanol.

The irradiation step may be carried out in an inert atmosphere. In thiscase the process is a pre-irradiation grafting process. The atmosphereis suitably nitrogen.

If irradiation is carried out in an inert atmosphere, it is desirable toremove in advance any dissolved oxygen from the reaction mixture beforethe polymer is added. This may be achieved by for example, purging themixture with nitrogen.

In the first embodiment, after the irradiation step, the irradiatedpolymer is immersed in the reaction mixture. Preferably, immersion issubstantially immediately or shortly after irradiation, although alonger interval between irradiation and immersion may still beeffective.

In a further embodiment, the irradiation step may be carried out in thepresence of oxygen. In this case, the process is a peroxide graftingprocess and suitably, further comprises a cleavage step after theimmersion of the irradiated polymer in the reaction mixture. Theperoxides or hydroperoxides are cleaved and grafting is initiated by forexample, heat, by the application of UV light, or by catalysis.

Irradiation of the polymer can be carried out with any suitable form ofionising radiation, suitably accelerated electrons. The radiation dosedelivered is dependent on the polymer and the specifications of thefinal product. Typically, the dose is in the range of 50 kGy to 300 kGy.

In the pre-irradiation embodiment of the process it can be useful to addsmall amounts of an initiator such as benzoyl peroxide. It may benecessary to heat the solution to cleave the initiators.

It may be beneficial to add cross-linkers. Di- or tri-functionalmonomers can cross-link the graft chains thus altering thecharacteristics of the final product. Suitable cross-linkers includedivinyl benzene, di- or tri(meth)acrylate and di- ortri(meth)acrylamide.

The polymer may be irradiated and then suspended in the reaction mixtureand permitted to react with the monomer. Alternatively, the polymer maybe suspended in the second phase and irradiated. The monomer (firstphase) may then be added to form the reaction mixture, or the secondphase containing the irradiated polymer may be added to the first phase.

The reaction, of monomer with irradiated polymer may be carried out atambient temperature, or at elevated temperature, e.g. up to 100° C.under ambient pressure.

After completion of the reaction, separation of the polymer is suitablyachieved, by filtering. Washing is preferably carried out to remove anyresidual monomer or homopolymer formed during the reaction. A suitablewashing procedure comprises firstly washing with ethanol, and then withdichloroethane or acidified water.

The grafting process according to the invention has many advantages. Theconversion of the monomers added to the graft solution is close to 100%,and thus expensive recovery and recycling of the monomers can bereduced. Accordingly, the process is more environmentally friendly sincethe formation of waste material is minimised. The process is also moreeasily controlled allowing variation from batch to batch to be avoided,leading to improved product quality.

By using the graft process according to the invention it is easy toprepare graft copolymers with a pre-determined capacity of functionalgroups. Monomer conversion is significantly higher than that which canbe achieved using conventional grafting techniques, giving a higherdensity of graft chains. Preferably, monomer conversion is greater than60%, more preferably greater then 70%, and in some cases greater than90%.

The graft copolymers can be further modified using conventional organicchemical reactions. For example, aminations, lithiations, chlorinations,brominations, esterifications, etherfications, Suzuki and Heck couplingsetc., can be used to provide chemically modified graft copolymers.

The graft copolymers or chemically modified graft copolymers can beloaded with one or more metals or metallic species to form catalyticallyactive materials. This may be achieved by any suitable method forexample, by immersing the graft copolymers in a solution of the metal ormetals of interest. Examples of suitable metals are known in the art andinclude the platinum group metals, such as Pt, Pd, Ru, Rh, Ir and Os,and transition metals, such as Fe and Ni. The performance of suchcatalysts can be tailored by changing the metal content, the ratio ofdifferent metals and the chemical functionality of the graft polymer.The catalysts so formed may be used for any suitable catalytic processor reaction for example, Suzuki-Miyaura couplings and Heck reactions.Catalyst supports comprising graft copolymers produced using the processdescribed herein form a further aspect of the present invention.

The skilled person will be able to see many ways of producing improvedgraft copolymers and chemically modified graft copolymers in accordancewith the invention.

It is believed that the invention provides novel graft copolymers usefulin many fields but especially in catalysis and ion-exchange to recoveror refine metals. Tests are ongoing to establish the definition and/oranalysis of such novel copolymers. It is the intention of the Applicantsto claim all novel processes, products and products derived from thepresent invention.

The invention will now be illustrated by way of example only.

EXAMPLE 1

350 g of cut polyethylene fibres (0.7 Dtex) were irradiated in an inertatmosphere to a total dose of 150 kGy using an electron acceleratoroperating at an acceleration voltage of 175 kV and beam current of 5 mA.The irradiated fibres were immediately immersed in a reaction mixturecontaining 203 g 4-vinyl pyridine, 412 g ethanol and 612 g water. Thereaction mixture was purged with nitrogen before initiating the reactionand the grafting reaction was allowed to continue to completion, whichtook approximately 6 hours.

The resulting fibres were filtered from the reaction mixture and washedwith ethanol and finally with dichloroethane or with an acidified watersolution. The weight gain of the recovered fibres was determined and theconversion of the monomer was calculated to be 100%.

EXAMPLE 2

Example 1 was repeated with a reaction mixture containing 200 g styrene,600 g ethanol and 400 g water. The conversion of the monomer wascalculated to be 82%.

EXAMPLE 3

Example 1 was repeated with a reaction mixture containing 203 g styrene,400 g ethanol and 600 g water. 3 g of divinyl benzene and 3 g of a 25 wt% solution of dibenzoyl peroxide were also added to the reactionmixture. The reaction took approximately 2 hours to reach completion.After the 2 hours the solution temperature was raised to 80° C. andmaintained there for 4 hours. The conversion of the monomer wascalculated to be 91.7%.

EXAMPLE 4

Example 1 was repeated with 223 g of cut polyethylene fibres (0.7 Dtex)and a reaction mixture containing 153 g styrene, 23 g vinyl benzylchloride, 588 g ethanol and 203 g water. The conversion of the monomerwas calculated to be 80%.

EXAMPLE 5

Example 1 was repeated with 134 g of cut polyethylene fibres (0.7 Dtex)and a reaction mixture containing 116 g styrene, 80 g vinyl benzylchloride, 166 g ethanol and 308 g water. 1 g of divinyl benzene and 1 gof a 25 wt % solution of dibenzoyl peroxide were also added to thereaction mixture. The conversion of the monomer was calculated to be99.5%.

EXAMPLE 6

Example 1 was repeated with 10 g of cut polyethylene fibres (0.7 Dtex)and a reaction mixture containing 20 g styrene, 5 g styryl diphenylphosphine, 50 g ethanol and 20 g water. 0.15 g of divinyl benzene and0.135 g of a 25 wt % solution of dibenzoyl peroxide were also added tothe reaction mixture. After the reaction was complete the temperaturewas raised to 80° C. for 1 hour. The conversion of the monomer wascalculated to be 76%. Elemental analysis of the copolymer gave aphosphorus content of 1.79%, indicating the extent of grafting of thestyryl diphenyl phosphine.

EXAMPLE 7

Example 1 was repeated with 10 g of cut polyethylene fibres (0.7 Dtex)and a reaction mixture containing 20 g styrene, 2 g styryl diphenylphosphine, 50 g ethanol and 20 g water. 0.02 g of divinyl benzene and0.2 g of a 25 wt-% solution of dibenzoyl peroxide were also added to thereaction mixture. After the reaction was complete the temperature wasraised to 80° C. for 1 hour. The conversion of the monomers wascalculated to be 91%. Elemental analysis gave a phosphorus content of0.76%.

EXAMPLE 8

Example 1 was repeated with 10 g of cut polyethylene fibres (0.7 Dtex)and a reaction mixture containing 20 g styrene, 0.5 g vinyl phenylboronic acid, 50 g ethanol and 20 g water. 0.03 g of divinyl benzene and0.2 g of a 25 wt-% solution of dibenzoyl peroxide were also added to thereaction mixture. After the reaction was complete the temperature wasraised to 80° C. for 1 hour. The conversion of the monomers wascalculated to be 93%.

EXAMPLE 9

9a Preparation of Palladium Catalyst

Polyethylene fibres modified with styrene/styryldiphenylphosphineco-polymer prepared according to the invention (60 g batch) were stirredin dichloromethane (480 ml). Palladium acetate (9.05 g, 1.25 equivalentsrelative to P in the polymer) was added. The mixture was stirred for twohours and the polymer fibres were then collected by filtration. Theywere washed thoroughly with dichloromethane and dried in air, then invacuo.

-   Yield: 67.9 g    9b Suzuki-Miyaura Coupling using Catalyst Prepared as above in 9a

The Pd catalyst (20 mg) was mixed with 4-bromoacetophenone (1M intoluene, 1.65 ml) phenylboronic acid (0.305 g) and potassium carbonate(0.449 g) in toluene (3.35 ml). The mixture was stirred and heated to70° C. under nitrogen. After two hours the solution was allowed to coolto room temperature and was filtered. Analysis of the filtrate by gaschromatography indicated complete conversion of 4-bromoacetophenone to4-acetylbiphenyl.

9c Heck Reaction using Pd Catalyst Prepared as above in 9a

The Pd catalyst (20 mg) was mixed with 4-bromoacetophenone (0.71 g)n-butyl acrylate (0.64 g) and sodium acetate (0.32 g) inN,N-dimethylacetamide (5 ml). The mixture was stirred and heated to 100°C. for 24 hours under nitrogen. The solution was allowed to cool and wasfiltered. Analysis of the filtrate by gas chromatography indicated 97%conversion of 4-bromoacetophenone to 4-acetyl-n-butylcinnamate.

COMPARATIVE EXAMPLE 1

Example 1 was repeated with 250 g of cut polyethylene fibres (0.7 Dtex)and a reaction mixture containing only 1040 g styrene. No water waspresent in the reaction mixture. The conversion of the monomer wascalculated to be 33%.

COMPARATIVE EXAMPLE 2

Example 1 was repeated with 100 g of cut polyethylene fibres (0.7 Dtex)and a reaction mixture containing only 460 g vinyl benzyl chloride and200 g ethanol. No water was present in the reaction mixture. Theconversion of the monomer was calculated to be 25%.

COMPARATIVE EXAMPLE 3

Example 1 was repeated with 115 g of cut polyethylene fibres (0.7 Dtex)and a reaction mixture containing only 427 g 4-vinyl pyridine and 210 gethanol. No water was present in the reaction mixture. The conversion ofthe monomer was calculated to be 18%.

1. A process for the production of a graft copolymer, the processcomprising reacting an irradiated polymer in a reaction mixturecomprising a first phase and a second phase; wherein the first phasecomprises a source of at least one non-water soluble monomer; whereinthe second phase comprises water; and wherein the first and secondphases are substantially immiscible and non-emulsified.
 2. A processaccording to claim 1, wherein the second phase further comprises a watermiscible organic solvent.
 3. A process according to claim 1, wherein thepolymer is a polyolefin or a fluorinated polyolefin.
 4. A processaccording to claim 1, wherein the at least one non-water soluble monomeris selected from the group consisting of: styrene and derivatives, vinylbenzyl derivatives, vinyl benzyl chloride, styryl diphenyl phosphine,vinyl benzyl boronic acid, vinyl benzyl aldehyde and derivatives,α-methyl styrene, α-methyl styrene derivatives, m-isopropyl-α,α-dimethylbenzyl isocyanate, vinyl acetate, vinyl pyridine and vinyl sulphonicacid.
 5. A process according to claim 1, wherein water comprises from 5to 80% by weight of the reaction mixture.
 6. A process according toclaim 5, wherein water comprises from 20 to 50% by weight of thereaction mixture.
 7. A process according to claim 2, wherein the watermiscible organic solvent comprises an alcohol.
 8. A process according toclaim 7, wherein the alcohol comprises ethanol.
 9. A process accordingto claim 1, wherein the polymer is irradiated in an inert atmosphere.10. A process according to claim 1, wherein the polymer is irradiated inthe presence of oxygen.
 11. A process according to claim 1, wherein thereaction mixture further comprises an initiator.
 12. A process accordingto claim 11, wherein the initiator comprises benzoyl perioxide.
 13. Aprocess according to claim 1, wherein the reaction mixture furthercomprises a cross-linker.
 14. A process according to claim 13, whereinthe cross-linker is selected from the group consisting of divinylbenzene, di- or tri- (meth) acrylate, or di-or tri-(meth) acrylamide.